Heterogeneities in the structure and function of the striatum (i.e., caudateputamen) have been described in recent years. Structurally, these islands of striatal tissue have been termed 'Striosomes'. The behavioral effects of damaging nigrostratal dopaminergic afferent fibers may depend upon the denervation of specific of these striosomes. The present experiments examine the possibility that the dopaminergic innervation to the striatum of the rabbit is heterogeneously organized. The experiments use a combination of histochemical techniques for localizing acetylcholinesterase, succinate dehydrogenase, and dopamine in the brain of the rabbit or rat.